The present invention relates to a position measuring apparatus, and particularly to a method of measuring the position or the distance of an object using a pair of image data obtained from the same object at difference positions or at different moments. The apparatus of this type is indispensable for a variety of equipment (such as robot having a sense of sight, automatic controller of a vehicle which responds to the external scenery, a process controller that works being interlocked to an ITV, and the like) which control devices relying upon image data.
In the position measuring apparatus of the above-mentioned type, it is necessary to determine by the automatic processing a point of one image which corresponds to a point of the other image. A conventional method for this purpose can be represented by "Cooperative Computation of Stereo Disparity" by D. Marr, T. Poggio, disclosed in "Science", Vol. 194,15, October, 1976, pp. 283-287. Another conventional method is represented by "Method of Forming Depth Data Signals for Three-Dimensional Televisions" disclosed in Japanese Patent Publication No. 10564/1985.
The above first conventional method permits the operations to be performed concurrently, and is adapted to high-speed processing. According to this method, however, the correspondence is not so fine since corresponding relationships are found among the pixels for the image consisting of pixels that are quantized into two levels. That is, a pixel of an image cannot be corresponded to an intermediate position between a pixel and a pixel of another image. This makes it difficult to calculate a position maintaining high precision. Further, since it is allowed to treat only those images that are quantized into two levels, the pixels are erroneously corresponded, and therefore develop many points which greatly deviated from the calculated positions.
The above second conventional method is also adapted to high-speed processing, in which two image signals are compared, and depth data of an object is obtained from the deviation between the pixels at a time when signal waveforms are nearly brought into agreement. In comparing the signal waveforms, however, one image that is being shifted is compared with another image. Therefore, the position is found even for a pixel of an object that has been projected upon one image only. In fact, however, the distance cannot be found for a portion (occluded region) that has been projected on one image only. In order to obtain position data maintaining high precision, therefore, it is necessary to correctly detect the occluded region and to remove it.